we will update this post to give available help materials on getting started with BizTalk EDI/As2.
Help material for BizTalk EDI/As2:
EDI tutorials (MSDN ): http://msdn.microsoft.com/en-us/library/bb259975.aspx
Good article to get started: http://msdn.microsoft.com/en-us/magazine/cc748658.aspx
Book on EDI/As2: http://www.amazon.com/Pro-EDI-BizTalk-Server-2006/dp/1590599357
EDI forum for asking any question: http://social.technet.microsoft.com/Forums/en-US/biztalkediandas2/threads
Understanding general Mapping on BTS 2009 and also EDI mapping challenges: http://www.springer.com/computer/programming/book/978-1-4302-1857-9